DULG

To prevent GDB from jumping around in the code when trying to
single step, i. e. when it seems as if the code is not executing
line by line, you can recompile your code with the following
additional compiler options:

-fno-schedule-insns -fno-schedule-insns2

On some systems (like the MPC8xx or MPC8260) you can only define
one hardware breakpoint. Therefore you must delete an existing
breakpoint before you can define a new one: